Division of Agronomy, Indian Agricultural Research Institute, New Delhi, India

Growth and Yield Responses of Short Duration Pigeonpea to Intercropping with Mungbean and Sorghum, and to Phosphate Fertilization

ANCHA SRINIVASAN and l. P. S. AHLAWAT

Authors' addresses: Dr. ANCHA SRINIVASAN, International Crops Research Institute for the Semi Arid Tropics, ICRISAT Patancheru P.O., A.P. India, 502 324; Dr. I. P. S. AHLAWAT, Division of Agronomy, Indian Agricultural Research Institute, Pusa, New Delhi, India, I 10 012.

With 3 figures and 4 tables

Received January 8, 1990; accepted May 27, 1990

A field experiment was conducted under rainfed conditions at the Indian Agricultural Research Institute, New Delhi, India with a view (i) to find out the possibility of introducing mungbean and sorghum as an intercrop with a short duration variety of pigeonpea, (ii) to assess the effects of planting geometry on the growth and productivity of pigeonpea and intercrops, and (iii) to study the effects of phosphate (P) fertilization on growth and yield components of pigeonpea in sole and intercropped systems.

Intercropping adversely affected the growth and yield performance of pigeonpea. Sorghum as an intercrop, however, offered more competition than mungbean. Planting geometry had no effect on growth and yield of pigeonpea but the productivity of intercrops per unit area was more in paired row pattern than in unlform row pattern largely because of a higher plant population in the former system. Pigeonpea and both intercrops responded favourably to P application. Pigeonpea as a sole crop responded significantly up to 60 kg P2O5 ha-1 only whlle the intercropped pigeonpea and intercrops continued to respond up to 90 kg. The implications of these results in relation to management of cropping systems are discussed.

Key words: Intercropping pigeonpea, Planting geometry, Phosphate fertilization, Growth and yield analysis, Sorghum, Mungbean.

Introduction

Intercropping of long duration pigeonpea (6-9 months) with grain legumes and cereals is a traditional practice followed in most parts of India (AIYER 1949, JODHA 1981). The advantages of this system in subsistence agriculture have been discussed at length by several workers (e.g., WILLEY 1979). The prolonged slow growth and developmental plasticity of pigeonpea in the system provides an excellent opportunity for growing early maturing intercrops so that early season resources (moisture supply, solar radiation etc.) can be used efficiently. Recently, however, short duration (4-5 months) high yielding pigeonpea varieties have been developed and it is not known clearly whether intercropping these with other crops would be feasible and remunerative as it has been with the long duration cultivars.

In most cases, the advantages of intercropping systems are not fully realized by farmers largely because of poor agronomic management. The benefits from intercropping can be improved not only by selecting compatible crop species and plant densities for component crops (WILLEY and RAO 1981) but also by adopting suitable planting geometry. The choice of appropriate planting arrangement minimizes both interspecific and intraspecific competition while allowing easy application of inputs. DE et al. (1978) indeed suggested that slight modifications in planting geometry of the base crop, without any decrease in plant population per unit area, would make intercropping feasible and often more profitable. However, little work has been conducted so far to study the effects of plantmg geometry on productivity of short duration pigeonpea.

Another important consideration in intercropping is nutrient management of the crops concerned because it is not possible to realize maximum productivity both in time and space without adequate supply of nutrients. AIthough intercropping is widely practiced in the arid and semi-arid tropics, information on fertilization practices is scarce. Wherever such information is available, it is concerned mainly with nitrogenous fertilizers and very little information is available on phosphorus (P) managernent. Supply of P is very important in legume-based cropping systems because P is considered the most important nutrient limiting pulse production (SARAF and GANGASARAN 1986). In addition, legumes do fix nitrogen (N) to meet most of their demands and the soils where pulses are grown generally have adequate potassium (K).

In view of the limited studies on the above aspects in short duration pigeonpea, the present investigation was undertaken with the following objectives:

(i) to examine the feasibility of intercropping short duration pigeonpea with mungbean or sorghum,

(ii) to assess the effects of altering planting geometry of the base crop on growth and yield of pigeonpea and intercrops, and

(iii) to analyse the effects of applied P on growth and productivity of pigeonpea in pure and mixed stands.

Materials and Methods

Experimental site

A field experiment was conducted under rainfed conditions at the Agronomy Farm of the Indian Agricultural Research Institute, New Delhi (28.4oN latitude; 77.1oE longitude and 228.6 m altitude). The climate of this place is semi arid and sub-tropical with extremes of hot (May-June) and cold (December-January) weather with an average annual precipitation of about 63.5 cm. The mean weekly air temperatures ranged from 16.4 to 35.4 oC during the cropping period. Of Ihe 46.0 cm rainfall received during the cropping season, 23.5 cm was received in the third week of July alone. The soil of the experi mental site was a slightly alkaline (pH 8.1) sandy loam having low amounts of organic matter (0.35% organic carbon), total N (0.04%), and available P (9.8 kg ha-1), and medium status of available K (168.2 kg ha-1).

Treatments and Crop Culture

The experiment was laid out in a split plot design with 3 replications. The treatments comprised factorial combinations of 3 cropping systems (sole pigeonpea, and pigeonpea intercropped with mung bean, or sorghum) and 2 planting patterns (uniform rows and paired rows) as main plots, and 4 Ievels of P (0, 30, 60 and 90 kg P2O5 ha-1) as sub plots. In the uniform row pattern, one row of intercrop was planted between 2 rows of pigeonpea spaced at 60 cm. In paired row system, however, population of intercrops was kept 50 % higher than in uniforrn row pattern by growing 3 rows between 2 pairs of pigeonpea with an inter-pair spacing of 90 cm and intra-pair spacing of 30 cm.

A basal dose of 20 kg N ha-1 (as urea) was broadcast as a starter dose for legumes. An additional dose of 30 kg N was placed at the side of the sorghum rows at 30 days after sowing (DAS) in plots with sorghum as an intercrop. P (as single superphosphate) was applied at the side of pigeonpea rows as per the treatments. Legume seeds were inoculated with appropriate rhizobium and treated with a fungicide, Captan (2.5 g kg-1 seed). Seedlings were thinned at 10 DAS to give inter-plant distance of 20, 15 and 10 cm in pigeonpea, sorghum and mungbean respectively. In sorghum, gap filling was also done simultaneously with additional seedlings raised. 5% Benzene hexachloride dust (20 kg ha-1) was uniformly broadcast over the experimental area before the final ploughing for protection against termites and ants. Later in the season, one spray each of Metasystox (0.05%) and Endosulfan (0.07%) was given against leaf eating caterpillars and pod borers such as Helicoverpa armigera. Two hand weedings were done at 25 and 50 DAS to keep the plots weed-free.

Salient features of varieties used

Pigeonpea (UPAS I2O): This cultivar, a selection from P4768, is a semi spreading, medium tall, and early maturing (140-150 days) variety suitable for double cropping in north western plain zone of India, Pods are about 4-6 cm long, containing 3-4 small, yellow-brown seeds per pod.

Mungbean (PS 16): It is a direct selection from P596 and is known for synchronous maturity with a duration of 60-65 days. Plants are medium tall (45-50 cm) with an erect and profuse branching. Pods are slightly hairy with medium sized, green seeds .

Sorghum (CSH 6): This coordinated sorghum hybrid is a derivative of cross between MS2219A and CS 3541. It matures in about 110-120 days. Seeds are spherical and cream coloured, and do not deteriorate even when the crop is caught in rains.

Growth and yield analysis

Ten randomly selected plants were tagged in each plot for measuring height and number of branches periodically and were used for yield analysis at harvest. In addition, 5 plants were sampled periodically for determining leaf area and dry matter (DM) production. However, for brevity and clarity in presentation, only those data pertalning to early vegetative growth (45, 35 and 30 DAS in pigeonpea, sorghum and mungbean respectively), mid-flowering (90, 70 and 50 DAS in pigeonpea, sorghum and mungbean respectively), and harvest stages are discussed in this paper. Leaf area per plant in pigeonpea and mung bean was estimated using the relationship between DM and area of sample leaves in varying sizes. In sorghum, however, leaf area was estimated using all leaves. Area of leaflets/leaves was measured using a leaf area meter (Hayashi Denkoh Co. Ltd., Tokyo, Japan). The leaf area values obtained for different crops were used to calculate their respective leaf area indices (LAI). Separated plant parts were oven dried at 80oC for 48 h and weighed. The total DM per plant was then calculated.

For yield analysis, crops were harvested when about 90 % pods/grains were ripe. Grain and stalk yields per hectare were computed based on the yields obtained from net plots. Harvest index (HI) was then computed as the ratio of seed yield to total above-ground DM, excluding fallen leaves. For yield component analysis, number and weight of pods per plant and seed weight per plant were determined. From these values, husk weight per plant, mean weight of pod, seed and husk weights per pod were calculated. Seed number per pod was determlned using 50 randomly selected pods. In sorghum, length of spike was recorded. For determining test weight, 1000 grains of each crop were counted and their weight recorded. The total production was determined by converting the grain yield of intercrops into pigeonpea equivalent (PE) based on market prices prevailing at harvest.

Statistical analysis

Data for pigeonpea were subjected to statistical scrutiny by analysis of variance as per the methods suggested by PANSE and SUKHATME (1961). For intercrops, however, only mean values were presented .

Results and Discussion

A: Effects of Cropping system

Intercropping adversely affected grain and stalk yields of pigeonpea (Fig. 1). On an average, grain yield was reduced by 6.5 and 70.7% due to intercropping with mungbean and sorghum respectively. This reduction may be due to interspecific competition for both below-ground (soil moisture, nutrients, etc.) and above-ground (solar radiation, etc.) resources. Between two intercrops, however, sorghum offered more competition than mungbean. Owing to its small canopy, and being leguminous in nature, mungbean perhaps did not compete too much with pigeonpea for resources. The relative compatibility of intercrops was also evident when HI and PE were considered. HI in pigeonpea-mungbean intercropping system was at par with that in sole pigeonpea and was higher than in pigeonpea sorghum intercropping. PE was, however, highest in pigeonpea-mungbean system and was lowest in pigeonpea-sorghum intercropping. The yield gain with mungbean as an intercrop more than compensated the yield loss of pigeonpea leading to an overall yield advantage.

The adverse effects of intercropping on grain and stalk yields were not because of reduction in plant population but were largely due to reductions in yield components (Fig. 2) and growth attributes (Table 1 and Table 2). Here again, the magnitude of reduction was greater when pigeonpea was intercropped with sorghum than with mungbean. The reduced pod weight in plants intercropped with sorghum was due to fewer pods per plant and reduccd weight per pod. Visual observations in this treatment indicated a reduced development of pods. Most of the pods set were small and contained few seeds. However, as seed number per pod in this trial was determined using a random sample of 50 pods, it was not possible to indicate whether pods at some positions were more affectcd than the others. The precise effects on seed number may be ascertained by using radiographic techniques in vivo and in vitro (PECHAN and MORGAN 1983).

The reduction in yield components of pigeonpea by intercropping with mungbean was, however, in contradiction to the results reported by GUPTA et al. (1979) and GIRI et al. (1980). These variations may be attributed to differences in growth habit and maturing duration of cultivars used. In this experiment, the short duration variety of pigeonpea, cv. UPAS 12O, could not probably compensate the loss of yield by competition from mungbean which occupied the land for about 65 days during the crop season. Other studies were largely concerned with medium and long duration cultivars, which may have compensated the yield loss by extra growth later in the season.

The reduced yield of pigeonpea in intercropping was again primarily related to decreased biomass production evident throughout crop growth (Table 1 and Table 2). There was no evidence, however, to suggest that intercropping led to any significant alteration in the pattern of growth or partitioning of DM. The vigorous growth coupled with a higher leaf area in pure stands might have intercepted solar radiation more effectively leading to a greater assimilation and DM production than in mixed stands. While intercropping with mungbean caused less drastic effects on growth, intercropping with sorghum led to development of small plants with a reduced branching, leaf area, and DM as compared with those in pure stands. Such a reduced crop growth in thc latter system may be attributed to a severe competition offered by fast growing sorghum. As the duration of the sorghum hybrid uscd in this trial was about 110-120 days, the active growth period of sorghum coincided exactly with the reproductive growth of pigeonpea when rnost yield components were being determined. In this connection, GIRI et al. (1980) reported that intercropping with fast growing pearl millet led to a reduced growth of pigeonpea while intercropping with soybean and groundnut had no adverse effects. SINGH et al. (1979), SOUNDARARAJAN and PALANIAPPAN (1979), YADAV and YADAV (1981), and HEGDE and SARAF (1982) also observed reduced growth of plgeonpea in vanous intercropping Systems. The development of fewer pods in plants intercropped with sorghum, which also recorded a smaller leaf area, suggests that pod and seed set depend on the supply of carbon assimilates from the leaves.

B: Effects of planting geometry

Pigeonpea: The pattern of plant arrangement had no significant effect on grain and stalk yields and on yield components. AHLAWAT et al. (1982) and BISHNOI et al. (1987) also reported similar results while evaluating various pigeonpea-based intercropping systems. Al though plants in the paired row pattern grew taller and accumulated more DM than those in the uniform row planting, particularly in early stages, there were no significant differences in pod and seed production. This could be due to a higher inter-row competition and mutual shading of plants in paired row system, especially during reproductive growth. The precise reasons for negligible effects of planting geometry on pigeonpea, however, need to be investigated further.

Intercrops: Planting geometry considerably influenced the growth, development and seed yields of mungbean (Table 3) and sorghum (Table 4). Plants in uniform row pattern were shorter, branched more profusely, accumulated more DM, and yielded more than those in paired row pattern. Such an improved plant performance in the former system may be attributed to a greater availability of land and thereby less competition for resources. On the contrary, leaf area index and total yields per unit area were higher in paired row systern largely because of maintenance of a 50% higher plant population and also probably due to an in-built energy harvest mechanism (DE et al. 1978). The increased plant height in paired row system might be due to a greater elongation of meristematic cells, which in turn may be an indirect effect of mutual shading owing to a higher plant density. CROOKSTON et al. (1975) reported similar responses in beans following exposure to shading.

C: Effects of phosphate application

Pigeonpea: P application significantly improved grain and stalk yields, yield components and growth attributes (Fig. 1, Fig. 2, Table 1, and Table 2). For example, application of 60kg P2O5 ha-1 increased plant height (13.1 cm), primary branches (2.4), dry matter (I I .6 g), pods/plant (13.6), test weight (3.9 g) and grain yield (0.39 t/ha) over the control. While the growth attributes continued to increase with increasing levels of P applied, thc yield components (pods/plant, seeds/pod and test weight) increased only up to 60 kg. Furthermore, the incremental response was more at lower Ievel of P than at higher levels. For example, the increase in grain yield following application of 30, 60 and 90 kg was 29.5, 45.1 and 47.9% respectively over the control.

A vigorous plant growth coupled with a greater assimilatory surface (as reflected by a higher LAI) in plants supplied with P probably led to a better development of yield components and seed yield. An improved HI following P application suggests that plants receiving P could partition a higher proportion of dry matter into seed. Visual observations indeed confirmed that P supplied plants flowered earlier and for a longer time than the controls. P application may also have promoted more extensive and deeper root system thus enabling the crop to extract the water from deeper soil layers which may be out of reach of the unfertilized crop due to its shallower root growth. In this connection, SINGH et al. (1983) demonstrated that pigeonpea receiving P could extract twice as much water from 60-90cm soil depth as compared to the crop raised without P application. The response to P application per se can be attributed to (a) the poor P status of soil of the experimental field and (b) the requirement of P by pigeonpea for successful completion of growth cycle.

Intercrops: The effects of P application on grain and stalk yields, yield components, and growth attributes were largely similar to those for pigeonpea. Progressive increase of all components with increasing levels of P application was noticed up to the maximum dose tried out in the experiment.

Interaction effects: Interactions between cropping systems and P fertilization were significant in some cases (Fig. 3). LAI, DM and pods/plant failed to increase beyond 6O kg in pure stands and in pigeonpea-sorghum intercropping while they increased linearly up to 90 kg in pigeonpea-mungbean intercropping. Comparable sced yields of pigeonpea were obtained with 30 kg in sole pigeonpea and 60 kg in pigeonpea-mungbean intercropping. Furthermore, the yield differences between two systems were marked at all levels except 90 kg. This indicates that to get pigeonpea yields similar to those in pure stands, intercropping system should be supplied with a higher level of P so as to compensate the yield loss by competition from mungbean. Stalk yield and PE failed to increase beyond 60 kg in sole pigeonpea and pigeonpea-mungbean. The dif ferences in PE between two systems were significant only at higher levels of P. This result suggests therefore that higher levels of P are necessary to realize yield advantages from in tercroppmg systems.

Implications:

Although intercropping has been a traditional and popular cultural practice, it has only recently become the subject of scientific study. The advantages of intercropping include higher combined yields, higher yield stability from season to season, better spread of production over the growth period, improved quality of products, reduced adverse effects of pests, higher returns, and better soil protection against erosion (ANDREWS 1972). As the growth duration and phenology of component crops is a major factor determining the success of intercropping systems, identification of crops with appropriate phenology is essential for realizing maximum productivity. Based on the results of this experimcnt, it may be suggested that the intercrop in short duration pigeonpea should be chosen in such a way that its active growth period does not coincide with reproductive growth of pigeonpea and that its growth has no adverse effects on development of leaf area because pod and seed set appear to depend largely on supply of carbon assimilates. It is therefore sensible to suggest that only crops, which occupy land for a short time (about 2 months) and complete life cycle faster, should be chosen as intercrops. In view of these considerations, intercropping of short duration pigeonpea with mungbean can safely be recommended in north India as the total yield from the systern is significantly higher than from sole crop, particular[y when supplied with a higher level of P. Besides a higher productivity, this system will serve twin objectives of overcoming weed infestation in the rainy season and efficient utilization of early season resourccs.

Sowing pigeonpea in normally recommended spacing of 60 cm would afford little opportunity for growing intcrcrops. A switchover to paired row system, however, accommodates at least 50 % higher population of intercrops without any adverse effects on productivity of pigeonpea. The results therefore suggest that simple modifications in planting geometry would improve the profitability of intercropprng systems.

Significant growth and yield responses of pigeonpea and intercrops to P application indicate that adequate supply of P is essential to realize optimal yields. In general, an intercropping system may not requlre additional fertilizer if only one component needs fertilizer and when there is little competition for nutrients between component crops. It is evident from the results, however, that both legume-legume and legume-cereal intercropping systems require higher levels (80-90 kg/ha) of P than sole crop thereby suggesting the existence of some competition for P supply between crops .

The results also suggest that response to applied P depends on the available P status of soil and P requirements of component crops. Crops vary in their fertilizer P requirements because of physiological (rate of phosphorus uptake, etc.) and morphological (root surface area, etc.) differences and detection of such variation is important in fertilizer managemcnt of cropping systems (DWYER and MOODY 1988). lndeed, based on the soil status and characteristics of the crops to be grown in combination, some basic concepts can be formulated to assist in determining the nutrient requirements for a particular cropping system (REDDY et al. 1983). However, one should be cautious against generalization as the responses to P differ from cultivar to cultivar, from one agroclimatic zone to other and from one soil to another. The P management strategies will obviously be different in soils with low levels of P from those with medium to high status P. Studies on uptake of nutrients by sole and mixcd stands, and attempts to elucidate the crop characteristics for matching the fertilizer needs of crop to economize and rationalize P application in different soil and agroclirnatic zones of the country are, therefore, urgently needed.

Conclusion:

Zusammenfassung

Wachstum und Ertragsreaktionen fruhzeitiger Taubenerbsen in einem Intercropping-Anbau mit Mung-Bohnen und Sorghum auf Phosphatdungung

Ein Feldexperiment wurde unter naturlichen Regenfallbedingungen an dem Indian Agricul tural Research Institute, New Delhi, Indien, ausgefuhrt, um die Moglichkeit der Verwendung von Mung-Bohnen und Sorghum als Intercrop-Arten im Anbau mit fruhzeitigen Sorten der Taubenerbse zu untersuchen und hierbei die Einflusse der Pflanzenverteilung auf das Wachstum und die Produktivit(t von Taubenerbse sowie der Intercrop-Arten hinsichtlich des Einflusses einer Phosphatdungung auf Wachstum und Ertragskomponenten von Taubenerbsen in Reinanbau und in einem Intercropping-System zu erfassen. Der Intercropping-Anbau wirkte sich auf Wachstum und Ertrag der Taubenerbse ungunstig aus. Mischanbau mit Sorghum wirkte sich starker (ungunstig) aus als der mit Mung-Bohne. Die Pflanzenverteilung hatte keinen Einflub auf Wachstum und Ertrag der Taubenerbse; die Produktivitat der Arten im Mischanbau bezogen auf die Flacheneinheit wirkte sich starker bei einer paarigen Anlage der Reihen als bei gleichmabiger Reihenverteilung aus; dies durfte auf die hohere Bestandesdichte in dem Doppelreihensystem zuruckzufuhren sein. Taubenerbse und die beiden Mischanbauarten reagierten g(nstig auf eine P-Dungung. Taubenerbse im Reinanbau reagierte signifikant bis zu einer Dungung von 60 kg P2O5/ha, wahrend im Intercropping-System eine Reaktion bis zu einer Menge von 9O kg P2O5/ha nachzuweisen war. Die Bedeutung dieser Ergebnisse im Hinblick auf das Management von Intercropping-Systemen wird diskutiert.

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